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Unformatted text preview: uced by an electronic clock that is built into the processor. Thus, the
speed with which an instruction is executed is also directly related to the chip's
clock speed, or number of pulses it uses each second. Different chips (even
different versions of a particular chip) are produced with different clock speeds.
For example, the Intel 80286 chip used in IBM's PS/2, models 50 and 60, ran at 10
million pulses per second (that is, its clock speed was 10 megahertz or 10 MHz). Similarly, the Motorola 68000 chip used in Apple's Macintosh system had a clock
speed of 7.83 MHz Most of earlier chips had clock speed in the range of 2 to 66
MHz. The typical clock speeds of the microprocessor chips in the Pentium family
are given in Figure 20.3. Note that the higher is the clock speed, the faster is the
processor because it can execute more instructions in a given unit of time.
Two other major techniques used by the microprocessor chip designers for better
performance are larger cache sizes and larger instruction sets supported by a chip.
For example, the Pentium Processor has 16 KB (16 Kilo Bytes) of cache, which is
used for caching both recently used instructions and data. The more recently
introduced Pentium Processor family chips (Pentium Processor with MMX
technology, Pentium II Processor, and Pentium III Processor) have separate caches
of 16 KB each for data and instructions. That is, they effectively have 32 KB
cache size. Larger separate internal caches for data and instructions improve
performance by reducing the average memory access time and providing fast
access to recently used instructions and data. The instruction and data caches
being separate can be accessed simultaneously. Furthermore, the Pentium II
Processor and Pentium III Processor chips also have a 512 KB of level-two cache
that further improves performance by allowing a large amount of recently used
instructions and data to be cached. There are two kinds of memory caches. A
level-one cache (known as L1 cache) is built into the CPU chip it...
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